In power dispatching automation, measurement and data acquisition for electric power physical quantities was performed by a Remote Terminal Unit (RTU) in the early days, and has been performed by substation integrated automation in recent years. It is performed by a measuring unit in a digital substation; by an electric energy meter or a distribution transformer terminal in power utilization automation (such as power utilization information system, intelligent power utilization); by a power distribution switch terminal in power distribution automation; or by a measuring and transducing unit in a generator excitation controller. In all the measuring units or terminals mentioned above, the measurement and data acquisition (simply referred to as “remote measurement” hereinafter) process is such that an AC current i and an AC voltage u are inputted and sampled at a predetermined sampling interval Δ (analog-digital conversion) to obtain a sampling value ik of the current and a sampling value uk of the voltage; other physical parameters, such as AC current effective value Ik, AC voltage effective value Uk, active power Pk, reactive power Qk (k=1, 2, . . . ) and the like, are then calculated from ik and uk, and Pk and Qk are accumulated to derive active electric energy Wk and reactive electric energy Vk; then, re-sampling is performed at an interval of M (also known as freezing of data by a timing designated by the receiving side) to output re-sampling values Ij, Uj, Pj and Qj of the electric power physical quantities to the receiving side. The receiving side can receive them locally or remotely. Local reception can occur within the same apparatus, or within a different apparatus deployed nearby. Remote reception occurs from a long distance. The received remote measurement data is applied on the receiving side.
In the above remote measurement process, the sampling interval Δ generally can satisfy the Shannon sampling theorem, that is, the sampling frequency fΔ=1/Δ>2×fc (where fc is the cut-off frequency of the sampled signal). Therefore, the calculated effect values of the physical quantities, such as Ik, Uk, Pk and Qk, do not have the aliasing problem. However, after the re-sampling, since the re-sampling frequency fW<fc does not satisfy the Shannon sampling theorem, there will be an aliasing of high frequency components into low frequency components and as a result, an aliasing error will arise.
Currently, new energy power generation, direct-current (DC) transmission and non-linear load have been increasingly prevalent, and harmonic wave content has been greater and greater in power systems. As a result, the aliasing error as mentioned above has become larger and larger. Since calculation of reactive power requires an assumption that the current and voltage are sinusoidal signals, the error of reactive power and reactive electric energy is even bigger, to an extent that cannot be ignored.
For the receiving side, the effect values of the fundamental wave components, i.e., Ij1, Uj1, Pj1 and Qj1, are more valuable than the effect values Ij, Uj, Pj and Qj. For three-phase AC, fundamental wave positive sequence components, i.e., I(1)j1, U(1)j1, P(1)j1 and Q(1)j1, are more valuable than three-phase effect values Ij, Uj, Pj and Qj. However, no measuring units or apparatuses of the prior art have outputted fundamental wave components and positive sequence components. As a result, it is difficult to apply electric power physical quantities at the receiving side.
Re-sampling in power applications is divided into three categories: (1) re-sampling of ik and uk to output ij and uj, which is called waveform re-sampling, with the re-sampling interval denoted by MW, and the output being waveform values; (2) quick re-sampling of Ik, Uk, Pk and Qk, which is called effective value re-sampling, with the re-sampling interval denoted by MT, and the output being effect values; (3) slow re-sampling of Ik, Uk, Pk and Qk, which is called steady state re-sampling, with the re-sampling interval denoted by MS, and the output being steady state values. Typically, MW<MT<MS.
Chinese Invention Patents ZL200910158375.x and ZL200910158370.7 (to Hao YuShan, entitled “CONTINUOUS PHYSICAL SIGNALS MEASUREMENT DEVICE AND METHOD”) provides steady state data remote measurement and full state data remote measurement for general physical data. However, the output frequency does not conform to the above re-sampling frequency. Also, too many contents are outputted. It is thus inconvenient to apply it directly to power automation systems.